For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (electrolyte electrode assembly) which includes an anode, a cathode, and a solid polymer electrolyte membrane interposed between the anode and the cathode. The electrolyte membrane is a solid polymer ion exchange membrane. Each of the anode and the cathode includes an electrode catalyst layer and a porous carbon layer. The membrane electrode assembly and separators (bipolar plates) sandwiching the membrane electrode assembly make up a unit cell. In use, generally, a predetermined number of unit cells are stacked together to form a fuel cell stack, which is mounted in a vehicle, for example.
In general, the fuel cell adopts the so-called internal manifold structure where supply passages and discharge passages extend through separators in a stacking direction. The fuel gas, the oxygen-containing gas, and the coolant are supplied from the respective supply passages respectively to a fuel gas flow field, an oxygen-containing gas flow field, and a coolant flow filed along electrode surfaces, and then, the fuel gas, the oxygen-containing gas, and the coolant are discharged into the respective discharge passages.
For example, in a fuel cell separator disclosed in Japanese Laid-Open Patent Publication No. 08-222237, as shown in FIG. 32, a separator plate 1 is provided. The separator plate 1 is a metal plate, and a large number of projections 2a, 2b are formed on front and back surfaces of the separator plate 1 by embossing or dimpling. Manifold loading ports 3a, 3b, 3c, and 3d for being loaded with respective gas manifolds, extend through the separator plate 1 outside an area having the projections 2a, 2b. 
For example, the gas manifold loading ports 3a, 3b, 3c, and 3d are used as a fuel gas inlet manifold, an oxygen-containing gas inlet manifold, a fuel gas discharge manifold, and an oxygen-containing gas discharge manifold.